And he was there when Gianni, 50, was shot by a gay serial killer on the steps of his lavish Miami home.

As the 20th anniversary of the ­killing approaches, a major TV series about the murder is being made, ­starring Penelope Cruz as fiery ­former drug addict Donatella.

Ex-model Antonio told The Sun on Sunday: “When Donatella first came into my life I tried to treat her like she was family but towards the end I thought of her as a monster.

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Antonio D'Amico was Gianni's loverCredit: Oliver Dixon

“Drugs fry your brain and Donatella became angry, frustrated and suspicious of the people around her. She was very difficult to deal with.

“I saw her as a diva who thought she was the genius in the family.

“But she was nothing compared to her brother.

“The hardest thing was she dropped Gianni’s name from the company.

“I could never understand how she could do that as for me it showed a complete lack of respect.”

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Penelope Cruz plays Donatella in the new showCredit: Splash News

Antonio, now 58, claims the family feud began when Elton John tipped off Gianni about Donatella’s drug use, which led the designer to sideline his sister in the business.

He says Gianni’s relationship with Donatella, who later admitted to an 18-year cocaine addiction, took a significant downturn in the early 1990s when he found out she had started using the drug at parties attended by model pals such as Naomi Campbell.

In our exclusive interview, he said: “Gianni was furious when he found out Donatella was on drugs. I was there when he took the phone call from Elton. He was shocked.

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Drama... Penelope Cruz with DonatellaCredit: Getty Images - FilmMagic

“Gianni was always anti-drugs and neither of us ever took coke so he could not believe his sister was doing it.

“But people had seen her taking drugs at a party in Los Angeles and Elton called him to pass on the news.

“Gianni immediately phoned Donatella and at first she denied it.

“But eventually her habit got so bad she had to go to rehab to get treatment.

“Gianni was disappointed in her and it caused him to lose trust in his sister. They always had a love-hate relationship and it became more fractured after that.

“I don’t think he was worried she would harm the house of Versace as he was in control and made all the decisions.

“But he did not have a high opinion of her as a designer or a businesswoman and would get upset by some of the things she did.”

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The scene of the shootingCredit: Reuters

The Versace empire was founded by Italian designer Gianni, who started out as an apprentice in his mother’s sewing business in 1978.

Over the years he turned his company into one of the biggest fashion houses in the world, worth around £2billion, with annual sales of more than £500million, and became friends with celebrities including Eric Clapton, Princess Diana, Madonna, Cher and Sting.

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Gianni's blood runs down the stepsCredit: AFP

He handed 30 per cent of his business to his older brother Santo, 72, and 20 per cent to his younger sister Donatella but by the early 1990s, according to Antonio, Gianni started to have serious concerns about Donatella’s ability to run the firm.

In 1996 he stated in a newspaper interview he was “at war” with his sister who had risen in the company to the point where she had become his rival.

At the same time he made his will. He divided his part in the company and his multi-million pound fortune between Antonio and Donatella’s children, daughter Allegra, now 30, and 26-year-old son Daniel.

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A talent lost... Gianni VersaceCredit: Getty Images - WireImage

Tragedy struck a year later when Gianni was shot on the steps of his Miami mansion by Andrew Cunanan, a 27-year-old “high-class” gay prostitute, who had carried out at least five random murders before this attack.

He took his own life as the police closed in on him eight days after he had murdered Gianni.

The shocking killing is being recreated for the TV series The Assassination Of Gianni Versace: American Crime Story.

It is currently shooting in Miami, where actress Penelope, 43, has been photographed wearing a red dress as she plays party-loving Donatella. Antonio is played by singer Ricky Martin, 45.

But Antonio says he has little faith the Hollywood studio will accurately portray what was really happening behind the scenes.

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Gianni and Antonio on holiday togetherCredit: Collect

He said: “In public Donatella was crying on my shoulder and in private she was treating me like s**t.

“I felt she was doing everything she could to get rid of me from the ­business.

“I don’t know why she hated me so much. You would have to ask her that. I rarely argued with her as I would always try to avoid her.

“Maybe she was jealous of me because I had power from being so close to Gianni and he would listen to me more than her.

“Donatella saw herself as the star of Versace.

“After her brother died she seemed to get rid of people he was close to. She is not a happy person in my opinion. She does not have many friends.”

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The dramatic death scenes from the show

Donatella has publicly admitted she does not like Antonio.

Two years after her brother’s death she reportedly said: “My relationship with Antonio is exactly as it was when Gianni was alive. I respected him as the boyfriend of my brother but I never liked him as a person. So the relationship stayed the same.”

Gianni left Antonio a small ­pension of around £20,000 a year in his will, as well as his multi-million pound homes in New York, Milan, Lake Como in Italy and Miami, where he was killed.

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Smoking... Penelope CruzCredit: Splash News

But Antonio, who now runs fashion label Antonio D’Amico Golf, says the money was eaten up by taxes and he decided to hand back the houses to the Versace family.

Donatella ­meanwhile remains vice president of the Versace group and took over as the designer after her brother’s death.

Too upset to talk about the details of the murder, Antonio added: “I gave back all the homes after Gianni died because I didn’t want to be anywhere near Donatella.

“She made it clear she did not want me around and so I left. It was my decision.

“I don’t care about material things and I did not want all that negative energy around me.

“After Gianni died I entered a very deep depression that lasted about five years. I’m not sure I would have got through it without the help of Elton John, who was the rock of support that I needed.

“It was Elton who encouraged me to get back to work and to keep designing clothes.

“Now I am living a humble life in a normal house in the countryside outside Milan. I am happy but I am not sure Donatella can say the same thing.

“Yes, she has helped make Versace a big company but for me it no longer has the touch of genius it had under Gianni. It has become mediocre, in my opinion.

“Donatella always thought she was brilliant but you can never have two geniuses in one family.”

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